You shouldn't have to change those 1ohm resistors for your application.
Also, you shouldn't have to change R3 or R4 for your application. I'd
use 1% resistors for those if you are super concerned about being as
close to 180v as possible.
The MC34063 has a rock solid 1.25v voltage reference for that feedback
line. One of the neat things about that SMPS controller IC.
-Adam
On 8/31/2011 7:48 PM, Ryan McDonald wrote:
Ok some questions about
http://threeneurons.files.wordpress.com/2011/08/mc34063_mk15cm1.gif
I plan to run the supply from 9v and need to get 180V at approx 13mA.
How do I go about choosing how many of the 1ohm R's to use? Do the .
9A, 1.2A, and 1.5A labels shown designate the required input current
from the supply?
I completely understand the equations surrounding R3 and R4 for
determining Vout. Lets say I use the default values shown, but end up
with 185V requiring me to adjust R3/R4 to get my desired 180V. How
would I decide which R to adjust "first"? I don't want to just
coarsely adjust R3 then compensate by fine tuning via R4. It seems to
me this undereducated approach would lead to the circuit getting "out
of balance" between R3 and R4. Can someone help me understand how I
would go about adjusting R3 and R4 *together* to get the desired
Vout? Again, I do understand how to calculate Vout given a R3 and
R4. What I want is to compute R3 and R4 to attain a given Vout.
Thanks!
-Ryan
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